Wednesday, July 2, 2014

Nazi Germany
had several codebreaking agencies both military and civilian. The armed forces
had separate agencies for the Army, Navy and Airforce plus there were
codebreaking departments in the Foreign Ministry, in Goering’s Forschungsamt
and in the Supreme Command of the Armed Forces. This last department operated
on civilian lines even though it was subordinated to the military.

The
OKW/Chi agency

OKW/Chi -
Oberkommando der Wehrmacht/Chiffrier Abteilung was the Signal Intelligence
Agency of the Supreme Command of the Armed Forces. It had been established as a
separate agency in 1920 and in the interwar period it was able to solve the
codes of many foreign countries. Initially the focus was on philological
research but the introduction of more complex codes and ciphers led the Germans
to invest in mathematical research in the field of cryptanalysis.

The person
who orchestrated this change in priorities was Wilhelm Fenner. Fenner started
working for the department in 1921 together with his friend Fedor Novopaschenny, a former Tsarist codebreaker
and in 1922 became an official employee. In the beginning he didn’t know much
about solving codes but he learned mathematical techniques from his Russian
friend and came to realize that the agency would need to make organizational
changes in order to solve the more difficult foreign cryptosystems.

Since Fenner
quickly became head of the cryptanalysis department he was able to carry out his
plan to reorganize the agency. First he introduced a more rigorous training
program for analysts and concentrated on the scientific analysis of cryptologic
history and systems.

The next step
in the 1930’s was to hire mathematicians.

Professor
Huettenhain and OKW/Chi’s mathematical research department

The first
mathematician hired by Fenner was Erich Huettenhain. In the mid 1930’s Huettenhain worked at the
observatory of the University of Münster and came to Fenner’s attention when he
contacted Chi with some of his proposals for cryptographic systems. Although
his systems were ‘unusable without
exception’ he was offered a job at Chi and he accepted.

Huettenhain became responsible for mathematical analysis of more
difficult cipher systems and in the early years of WWII new personnel were
hired to form a separate mathematical research department.

Apart from
the aforementioned individuals, two more mathematicians, Karl Stein
and Gisbert Hasenjaeger
were hired to work in the cipher security department.

Professors
Franz and the State Department’s strip cipher

According to
the recently declassified TICOM report DF-176 ‘Answers written by
professor doctor Wolfgang Franz to questions of ASA Europe’ Wolfgang Franz primarily
studied mathematics in the period 1924-1929, during 1930-1934 worked as an
assistant at the mathematical seminar at the University of Marburg and in 1937
moved to the University of Giessen as an assistant. When at the beginning of
WWII the University of Giessen was closed down he spent a semester as a
substitute at the University of Gottingen.

Thanks to a
friend of his who knew Huettenhain
he was able to get assigned to the OKW Cipher department in Berlin in 1940. The
initial training program consisted of solving simple codes and ciphers and as
Franz was easily able to cope with these he moved on to real traffic.

The first
systems he worked on were a Mexican and a Greek code and he was able to solve
them. The most important system solved by Franz was the US diplomatic M-138-A
strip cipher, called Am10 by the
Germans:

‘Especially
laborious and difficult work was connected with an American system which,
judging by all indications was of great importance. This was the strip cipher
system of the American diplomatic service which was subsequently solved in
part.’

According to
DF-176, p6 Franz had started his own investigations into this system and was
able to make some limited progress when he received the ‘circular’ strips 0-1
and three ‘special’ strips used between Washington and Helsinki, Tallinn and
Reval. Using these strips messages could be solved and his investigations could
move forward.

Thanks to the
success of the department is solving the strip cipher dr Huettenhain was able to hire more
mathematicians and expand the research section.

It is
interesting to note that a special cryptanalytic device called the ‘Tower-Clock’was used to
solve the strip system. Franz says in pages 9-10:

‘In addition, there was built at my suggestion
at the Bureau an electric machine which permits determining a number of
repetitions of letters in a polyalphabetic substitution on a width of 30 with a
depth of 20 to 80 lines, taking one line at a time, which naturally is
fundamental for problem (f) above.’

According to EASI
vol2 ‘Notes on German High level
Cryptography and Cryptanalysis’ , p56-57

c.
Statistical "depth-increaser." - The "Turmuhr," or
"Tower-Clock was a device for testing a sequence of thirty
consecutive cipher letters statistically against a given "depth" of
similar sequences, to determine whether the former belonged to the given depth.
It was used "primarily for work on the U.S. strip cipher, when cribbing which was generally employed
was impossible. It cost approximately $1,000.00.

The
apparatus consisted of a single teleprinter tape reading head (speed 1 1/2
symbols per second); a storage means, by which any one of five different scores
could be assigned, on a basis of frequency, to each of the letters in the 30
separate monoalphabets that resulted from the 30 columns of depth; a
distributor that rotated in synchronism with the tape stepping, and selected
which set of 30 scores was to be used as basis for evaluating the successive
cipher letters; and a pen recording device.

‘This strip cipher system, when rightly
employed, doubtlessly has great advantages .It appears to me, however, that it
was not used with sufficient caution. Only through carelessness, in part
through lack of care in setting up, was it possible to break into the system as
far as we did. Only after the Americans had obviously noticed that many of
their messages were being read was the application so modified that although
the basic idea was the same the possibilities of breaking in were materially
reduced.’

Postwar
career

In the
postwar period professor Franz returned to teaching at Frankfurt University
where he eventually became dean of the newly established Department of
Mathematics. Also in 1967 he became president of the German Mathematical
Society.

In the end It
might give some comfort to the Americans to know that their strip cipher was
solved by a real gentleman, as report DF-176 says: ‘Personal contact with Dr Franz indicated that he was a gentleman of
unusual scholarship and integrity, an impression confirmed by the report’.